Sensitive Affimer and Antibody Based Impedimetric Label-Free Assays for C-Reactive Protein

C-reactive protein (CRP) is an acute phase protein whose levels are increased in many disorders. Levels greater than 3 mu g/mL serum have hitherto been considered to indicate pathology, but there is increasing interest in assessments between 0.1 and 10 mu g/mL, which have been found to correlate with severity of risk for cardiovascular disease. We report herein the generation of both antibody and Affimer based impedance immunoassays for CRP that are substantially more sensitive than clinically utilized immunonephelometry and immunoturbidity assessments. Significant in this study is not only the use of a constrained peptide to detect a clinically important target but also that derived electrochemical impedance assays can be highly sensitive even with probes whose relatively weak (mu M) affinities are not amenable to target detection by surface plasmon resonance (SPR). Key to this finding is acknowledging that receptive surfaces of comparatively low initial steric bulk and charge transfer resistance are especially primed to be highly responsive to target binding in electroanalytical assays of this type.

Luminescence of Tb(3+) doped TeO(2)-ZnO-Na(2)O-PbO glasses containing silver nanoparticles

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Variable structure control of switched systems based on Lyapunov-Metzler-SPR systems

This paper presents two Variable Structure Controllers (VSC) for continuous-time switched plants. It is assumed that the state vector is available for feedback. The proposed control system provides a switching rule and also the variable structure control input. The design is based on Lyapunov-Metzler (LM) inequalities and also on Strictly Positive Real (SPR) systems stability results. The definition of Lyapunov-Metzler-SPR (LMS) systems and its direct application in the design of VSC for switched systems are introduced in this paper. Two examples illustrate the design of the proposed VSC, considering a plant given by a switched system with a switched-state control law and two linear time-invariant systems, that are not controllable and also can not be stabilized with state feedback. ©2008 IEEE.

Plasmonic structures fabricated by interference lithography for sensor applications

In this work we demonstrate the use of holographic lithography for generation of large area plasmonic periodic structures. Submicrometric array of holes, with different periods and thickness, were recorded in gold films, in areas of about 1 cm2, with homogeneity similar to that of samples recorded by Focused Ion Beam. In order to check the plasmonic properties, we measured the transmission spectra of the samples. The spectra exhibit the typical surface plasmon resonances (SPR) in the infrared whose position and width present the expected behavior with the period of the array and film thickness. The shift of the peak position with the permittivity of the surrounding medium demonstrates the feasebility of the sample as large area sensors. © 2009 SPIE.

On the photonic dispersion of periodic superlattices made of left-handed materials

Studies of the band gap properties of one-dimensional superlattices with alternate layers of air and left-handed materials are carried out within the framework of Maxwell's equations. By left-handed material, we mean a material with dispersive negative electric and magnetic responses. Modeling them by Drude-type responses or by fabricated ones, we characterize the n(ω) = 0 gap, i.e., the zeroth order gap, which has been predicted and detected. The band structure and analytic equations for the band edges have been obtained in the long wavelength limit in case of periodic, Fibonacci, and Thue-Morse superlattices. Our studies reveal the nature of the width of the zeroth order band gap, whose edge equations are defined by null averages of the response functions. Oblique incidence is also investigated, yielding remarkable results. © 2010 Springer Science+Business Media B.V.

Study of Er3+ fluorescence on tellurite glasses containing Ag nanoparticles

Optical characteristics of tellurite glasses containing silver nanoparticles (NPs) and the influence on the emission spectrum of Er 3+ ions were studied. The transitions 4f ↔ 4f from erbium ions, mainly the 4I13/2 → 4I15/2 transition that involve upconversion energy process, have a strongly dependence with the chemical structure of the rare earth ion. In the present work, silver nanparticles (NPs) embedded in the host vitreous material, show a significant enhance (or quenching) on the erbium fluorescence due the long-range electromagnetic interaction between the plasmon surface energy of the Ag NPs (Localized Surface Plasmon Resonance -LSPR) and the Er3+ ions.

Tethered DNA scaffolds on optical sensor platforms for detection of hipO gene from Campylobacter jejuni

DNA biosensors have gained increased attention over traditional diagnostic methods due to their fast and responsive operation and cost-effective design. The specificity of DNA biosensors relies on single-stranded oligonucleotide probes immobilized to a transduction platform. Here, we report the development of biosensors to detect the hippuricase gene (hipO) from Campylobacter jejuni using direct covalent coupling of thiol- and biotin-labeled single-stranded DNA (ssDNA) on both surface plasmon resonance (SPR) and diffraction optics technology (DOT, dotLab) transduction platforms. This is the first known report of the dotLab to detect targeted DNA. Application of 6-mercapto-1-hexanol as a spacer thiol for SPR gold surface created a self-assembled monolayer that removed unbound ssDNA and minimized non-specific detection. The detection limit of SPR sensors was shown to be 2.5 nM DNA while dotLab sensors demonstrated a slightly decreased detection limit of 5.0 nM (0.005 μM). It was possible to reuse the SPR sensor due to the negligible changes in sensor sensitivity (∼9.7 × 10 -7 ΔRU) and minimal damage to immobilized probes following use, whereas dotLab sensors could not be reused. Results indicated feasibility of optical biosensors for rapid and sensitive detection of the hipO gene of Campylobacter jejuni using specific ssDNA as a probe. © 2011 Elsevier B.V.

Electrochemical studies based on local interfacial ph changes of gold nanoparticles immobilized on polystyrene brushes

The electrochemical behavior of polystyrene modified with gold nanoparticle (Au NPs) was investigated in terms of pH-responsive polymer brush. A pH-responsive of modified polymer brush from tethered polystyrene was prepared and used for selective gating transport of anions andcations across the thin-film. An ITO-coated glass electrode was used as substrate and applied to study the switchable permeability of the polymer brush triggered by changes in pH of the aqueous environment. The pH-sensitive behavior of the polymer brush interface has been demonstrated by means of cyclic voltammetry (CV) and Localized Surface Plasmon Resonance (LSPR). CV experiments showed at ph values of 4 and 8 induces swelling and shrinking of the grafted polymer brushes, respectively, and this behavior is fast and reversible. LSPR measurements showed a blue shift of 33 nm in the surface resonance band changes by local pH. The paper brings an easy methodology to fabrication a variety of nanosensors based on the polymer brushes-nanoparticle assemblies. © 2013 by ESG.

SERS mapping in langmuir-blodgett films and single-molecule detection

Plasmon-enhanced spectroscopic techniques have expanded single-molecule detection (SMD) and are revolutionizing areas such as bio-imaging and single-cell manipulation. Surface-enhanced (resonance) Raman scattering (SERS or SERRS) combines high sensitivity with molecularfingerprint information at the single-molecule level. Spectra originating from single-molecule SERS experiments are rare events, which occur only if a single molecule is located in a hot-spot zone. In this spot, the molecule is selectively exposed to a significant enhancement associated with a high, local electromagnetic field in the plasmonic substrate. Here, we report an SMD study with an electrostatic approach in which a Langmuir film of a phospholipid with anionic polar head groups (PO 4 -) was doped with cationic methylene blue (MB), creating a homogeneous, two-dimensional distribution of dyes in the monolayer. The number of dyes in the probed area of the Langmuir-Blodgett (LB) film coating the Ag nanostructures established a regime in which single-molecule events were observed, with the identification based on direct matching of the observed spectrum at each point of the mapping with a reference spectrum for the MB molecule. In addition, advanced fitting techniques were tested with the data obtained from micro-Raman mapping, thus achieving real-time processing to extract the MB single-molecule spectra. © 2013 Society for Applied Spectroscopy.

Nonlinear Optical Properties of Tungsten Lead-Pyrophosphate Glasses Containing Metallic Copper Nanoparticles

We have prepared heavy metal oxide glasses containing metallic copper nanoparticles with promising nonlinear optical properties which were determined by Z-scan and pump-probe measurements using femtosecond laser pulses. For the wavelengths within the plasmon band, we have observed saturable absorption and response times of 2.3 ps. For the other regions of the spectrum, reverse saturable absorption and lifetimes shorter than 200 fs were verified. The nonlinear refractive index is about 2.0 × 10-19 m2/W from visible to telecom region, thus presenting an enhancement effect at wavelengths near the plasmon and Cu+2 d-d band. © 2013 Springer Science+Business Media New York.

A immunosensor for the diagnosis of canine distemper virus infection using SPR and EIS

Canine distemper virus (CDV) is a viral disease that affects dogs and many other carnivores. Clinical diagnosis of CDV is difficult due to the broad spectrum of signs that may be confounded with other respiratory and enteric diseases of dogs. Laboratory analysis is required to diagnose suspected cases. In this study, surface plasmon resonance (SPR) and electrochemical impedance spectroscopy (EIS) methodologies were developed for the detection of canine distemper virus simultaneously. The assay exhibited high specificity, as all the negative controls were not mistakenly detected. The CDV concentration was determined from successive injections into the apparatus, with a linear range from 1.1 to 116.0 ng mL-1. The system exhibited good reproducibility with 4.5% variation between runs after regeneration of the coated surface with a solution of 0.1 M glycine-HCL (pH 3.0). The capacitance and resistance values of the modified interface were calculated from EIS data using an equivalent circuit. It was possible to measure CDV in highly concentrated viruses with good specificity and reproducibility. © 2013 The Royal Society of Chemistry.

Estudo da incorporação de particulas metálicas em vidros fosfato contendo tungstênio

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Modelagem de efeitos plasmônicos em um metamaterial nanoestruturado para aplicação em sensoriamento óptico

Metamateriais são meios artificiais estruturados para a obtenção de propriedades físicas não prontamente encontradas na natureza. Estes meios, em geral, são organizados periodicamente com uma célula unitária que possui dimensões menores que o comprimento de onda da radiação eletromagnética incidente. Esta característica permite que estes meios possam ser tratados como materiais homogêneos e, por conseguinte, descritos em termos de parâmetros constitutivos efetivos. Este trabalho realiza a modelagem analítica e numérica de um metamaterial nanoestruturado com inclusões metálicas. É desenvolvido um formalismo fundamentado no modelo de Maxwell-Garnett para descrever o índice de refração efetivo do metamaterial levando em conta a forma geométrica das nanopartículas e a natureza dos modos locais excitados. É evidenciado que estes modos correspodem a excitações plasmônicas superfíciais. Por meio da caracterização do metamaterial no domínio óptico, é investigado o potencial de tais meios para o desenvolvimento de sensores de índice de refração mais compactos e com valores de sensibilidade superiores aos encontrados em sistemas baseados unicamente em fibras ópticas.

Polymer brush modified electrode with switchable selectivity triggered by pH changes enhanced by gold nanoparticles

In this work, a sensor was built up with smart material based on polymer brush and gold nanoparticles. The modified electrode functionalized with polyacrylic acid (PAA) tethered to indium tin oxide (ITO) and covered with gold nanoparticle (ITO/PAA/Au) demonstrated switchable interfacial properties discriminating different pHs. The switchable electrochemical and plasmonic process was characterized by cyclic voltammetry (CV), electrochemistry impedance spectroscopy (EIS), and localized surface plasmon resonance (LSPR).

Alkylation of Histidine Residues of Bothrops jararacussu Venom Proteins and Isolated Phospholipases A(2): A Biotechnological Tool to Improve the Production of Antibodies

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)